Metal laminate and method of etching the same

ABSTRACT

The present invention relates to a metal laminate which is broadly used for a flexible wiring board or the like and an etching method therefor. In particular, the present invention relates to a metal laminate which includes a layer obtained by laminating a metal layer and an insulating layer, where the insulating layer is subjected to an etching process, wherein, in a surface of the metal layer which is positioned so as to come in contact with the insulating layer, respective concentrations of main metal element and oxygen element constituting the metal layer are measured from the surface of the metal layer towards inside of the metal layer in a time-elapsing manner according to AES (Auger electron spectroscopy) and a value of the thickness of a metal oxide film of the surface of the metal layer measured at a time when atomic concentrations of the main metal element and the oxygen element constituting the metal layer become equal to each other is in a range of at least 0 Å to less than 50 Å. According to the present invention, an etching time of polyimide in the polyimide metal laminate can be calculated and a flexure used for a suspension for a hard disc drive having a high productivity can be provided.

TECHNICAL FIELD

The present invention relates to a metal laminate which is broadly usedfor a flexible wiring board or the like and an etching method therefor.In particular, the invention relates to a metal laminate where aninsulating layer is excellent in etching property and which is suitablefor a high density circuit board material, and an etching methodtherefor.

RELATED BACKGROUND ART

Conventionally, for a flexure used for a suspension for a hard disc, apolyimide metal laminate mainly comprising copper alloy/polyimide/SUS304is used. Particularly, according to capacity increase and densificationin a hard disc in recent years, an amount of suspension use isincreasing. Therefore, in order to improve production efficiency,suspension processing makers have endeavored to achieve a highefficiency in each manufacturing step.

However, in case that the above-described polyimide metal laminate isused, there occurs such a problem that, in a step that polyimide isetched after SUS 304 developing a suspension function has been etchedwith aqueous solution of ferric oxide, when a polyimide etching isperformed, an etching rate varies for each lot of SUS304. For thisreason, in order to realize a secure polyimide etching, a polyimideetching over a long term is required, which prevents a high efficiencyfrom being attained.

As etching of polyimide, there are a method employing a dry etchingwhere etching is conducted using plasma gas such as NF₃, SF₆ or the like(refer to JP2002-25027A) and a method employing a wet etching wherestrong alkaline solution such as hydrazine solution, potassium hydroxidesolution or the like (JP2001-55570A). Even in case that either one ofthe etching methods is used, an etching rate of polyimide coming incontact with SUS304 varies according to respective lots of SUS304 to beused. For this reason, in order to conduct polyimide etching completely,it is necessary to set an etching time to be long so as to meet a casethat the etching rate is slow. In such a polyimide etching over a longtime, a phenomenon where polyimide is etched excessively over apredetermined size, so-called over-etching phenomenon is observed.Therefore, not only a problem that the above-described long time etchingis required occurs but also there occurs a problem in etching shape.

As an example where wet-etchable polyimide base resin is used, a metallaminate such as described in JP2002-240193A publication orJP2002-245609A publication has been proposed. According to theproposals, there is described that the metal laminate improves aproductivity and it is effective for cost reduction, because a wetetching rate of polyimide is fast. In these patent applications,however, there is not any clear description about an oxide film ofmetal, and there is a problem that according to circumstances, anetching rate of polyimide becomes slow and the so-called over-etchingphenomenon is caused, which results in deterioration of a shape andreduction in productivity. Further, since many wet-etchable polyimideshave an average thermal expansion coefficient of 25 ppm/° C. or more, adifference in thermal expansion coefficient between the wet-etchablepolyimide and metal material such as stainless steel or the like islarge and the polyimide is poor in warp or size stability, it isactually difficult to use such a polyimide as suspension material.

SUMMARY OF THE INVENTION

In view of the above-described problems, an object of the presentinvention is to provide a metal laminate where an etching rate of aninsulating layer can be improved stably after metal has been etched, andto provide an etching shape can be kept constant, and a metal laminatewhich allows variations in etching rate to be cancelled, and an etchingmethod of the same.

As results of an eager studying, the present inventors noticed a surfaceoxide film of metal existing in a lamination interface between aninsulating layer and a metal in a metal laminate comprising the metaland the insulating layer, and found that the thickness of the surfaceoxide film influences an etching rate or variations therein andtherefore a shape of etching or the like. And the present inventors havecompleted the present invention by making the above-described influenceclear.

That is, according to the present invention, there are provided:

1) A metal laminate which includes a layer obtained by laminating ametal layer and an insulating layer, where the insulating layer issubjected to an etching processing, wherein, in a surface of the metallayer which is positioned at a such a side that the metal layer comes incontact with the insulating layer, respective concentrations of mainmetal element and oxygen element constituting the metal layer aremeasured from the surface of the metal layer towards inside of the metallayer in a time-elapsing manner according to AES (Auger electronspectroscopy) and a value of the thickness of a metal oxide film of thesurface of the metal layer measured at a time when atomic concentrationsof the main metal element and the oxygen element constituting the metallayer become equal to each other is in a range of at least 0 Å to lessthan 50 Å.

2) The metal laminate according to the above 1), where the metal layercontains at least one of elements selected from the group consisting ofiron element, copper element, aluminum element, nickel element andmolybdenum.

3) The metal laminate according to the above 1), where the insulatinglayer comprises resin selected from the group consisting of polyimide,polyamide, and polyamideimide.

4) The metal laminate according to the above 1), where constitution ofthe metal laminate is a double-sided metal laminate comprising a metallayer/a polyimide layer/a SUS layer selected from the group consistingof copper, SUS and copper alloy.

5) The metal laminate according to the above 4), where the polyimidecomprises constitution of thermoplastic polyimide/non-thermoplasticpolyimide/thermoplastic polyimide.

6) A flexure used for a suspension for a hard disc, which ismanufactured from a metal laminate according to any one of the above 1)to 5).

7) A method for manufacturing a metal laminate which includes a layerobtained by laminating a metal layer and an insulating layer to eachother and where the insulating layer is subjected to an etchingprocessing, wherein, when an insulating layer is laminated on metal, ina surface of the metal layer which is positioned on such a side that themetal layer comes in contact with the insulating layer, respectiveconcentrations of main metal element and oxygen element constituting themetal layer are measured from the surface of the metal layer towardsinside of the metal layer in a time-elapsing manner according to AES(Auger electron spectroscopy) and metal meeting the condition that avalue of the thickness of a metal oxide film of the surface of the metallayer measured at a time when atomic concentrations of the main metalelement and the oxygen element constituting the metal layer become equalto each other is in a range of at least 0 Å to less than 50 Å isselected and used.

8) A plasma etching method according to any one of the above 1) to 5),where a metal laminate is used as a material to be etched.

9) A wet etching method of a metal laminate wherein a metal laminateaccording to in any one of the above 1) to 5) is etched with alkalinesolution.

According to the above, an etching time of polyimide in a polyimidemetal laminate can be calculated and a flexure with a high productivityused for a suspension for a hard disc drive can be provided.

DESCRIPTION OF PREFERRED EMBODIMENT

The present invention will be explained below in detail.

The present invention relates to a metal laminate which includes a layerobtained by laminating a metal layer and an insulating layer, where theinsulating layer is subjected to an etching processing, wherein, in asurface of the metal layer which is positioned at such a side that themetal layer comes in contact with the insulating layer, respectiveconcentrations of main metal element and oxygen element constituting themetal layer are measured from the surface of the metal layer towardsinside of the metal layer in a time-elapsing manner according to AES(Auger electron spectroscopy) and a value of the thickness of a metaloxide film of the surface of the metal layer measured at a time whenatomic concentrations of the main metal element and the oxygen elementconstituting the metal layer become equal to each other is in a range ofat least 0 Å to less than 50 Å.

The AES means Auger electron spectroscopy, and it can measure the kindand the amount of element existing on a solid surface by measuring Augerelectrons generated when the electron beam is irradiated. In the presentinvention, when atom concentrations of oxygen element and main metalelement constituting metal have become equal to each other, a thicknessfrom the metal surface inwards is measured as a thickness of a surfaceoxide film of the metal by using a TEM (transmission electronmicroscope) or a SEM (scanning electron microscope) or the like. In casethat SUS304 is used as the metal, elements detected by AES are oxygenelement (O) and iron element (Fe).

In the present invention, it is important that the thickness of surfaceoxide of metal is at least 0 Å and less than 50 Å. The thickness ispreferably at least 25 Å and 50 Å, and further preferably 30 Å and lessthan 40 Å. The Thinner the surface oxide is, the more preferable it is,because the etching rate becomes faster. However, when the surface oxideis thinner than 25 Å, a heat resistance thereof deteriorates, and whenthe surface oxide is exposed to a high temperature of 200° C. or higher,a discoloration may occur, to which attention should be paid. Further,since the etching rate of the insulating layer varies due to variationsin thickness of the surface oxide, it is preferable that the thicknessof the surface oxide is constant. On the other hand, when the thicknessof the surface oxide is 50 Å or more, such a drawback occurs that theetching rate of the insulating layer becomes considerably slow and aproductivity is much deteriorated, which is undesirable. Further, sincethe etching rate is fast, the so-called over-etching phenomenon is easyto occur, which makes it impossible to conduct micro-fabrication, forexample, fabrication of a line-shape with a width of 30 μm. As a result,it becomes difficult to meet size reduction of a suspension required formicro-fabrication, which is not desirable.

The thickness of the oxide film observed when the atom concentrations ofthe oxide element and the main metal element detected according to thetime elapsing by AES become equal to each other can be observed by TEM,SEM or the like. The TEM is a transmission electron microscope, whichallows observation of a surface and a section of a superfine portion,and analysis of a structure and element of the portion, andspecifically, which irradiates an electron beam on a thinned sample toimage electrons transmitted through the sample thereby allowingobservation. The SEM is a scanning electron microscope.

The metal in the metal laminate of the present invention is preferablymetal including at least one selected from the group consisting of ironelement, copper element, aluminum element, nickel element and molybdenumelement, and the metal is specifically one selected from the groupconsisting of copper, nickel, aluminum, stainless steel or alloythereof. The metal is preferably stainless steel and further preferablySUS304.

In case that SUS304 is used as the metal, control of a surface oxidefilm of SUS304 can be performed by adjusting a temperature and a time ina tension-anneal treatment where a material is left as it is for aconstant time in nitrogen gas atmosphere including hydrogen gas under ahigh temperature while a pulling tension is applied to the material inorder to conduct strain removal from the material rolled to be thin.Since the thickness of the surface oxide film is increased/decreasedaccording to oxidation/reduction reaction during the tension-annealtreatment, it is preferable that a treatment at a high temperature andfor a long time is conducted in order to thin the thickness. Preferableconditions of the tension-anneal treatment include a temperature of1000° C. to 1200° C. and a time of 10 minutes to 20 minutes.

In the present invention, the thickness of the metal is preferably 2 to150 μm, and more preferably 10 to 100 μm.

As the insulating layer in the metal laminate of the present invention,specifically, for example, a resin selected from the group consisting ofpolyimide, polyamide, polyamideimide or the like is given. Theinsulating layer is preferably polyimide, and it is further preferablethat the polyimide has a constitution of thermoplasticpolyimide/non-thermoplastic polyimide/thermoplastic polyimide.

It is preferable that the insulating layer in the metal laminate of thepresent invention is a single layer structure of thermoplastic resin andnon-thermoplastic resin, or a multi-layer structure constituted by acombination thereof.

Further, as the insulating layer in the metal laminate of the presentinvention, it is preferable that an average thermal expansioncoefficient thereof is at least 10 ppm/° C. and at most 25 ppm/° C. Theaverage thermal expansion coefficient is more preferably at least 15ppm/° C. and at most 20 ppm/° C. When the average thermal expansioncoefficient is in this range, an average linear expansion coefficient ofthe insulating layer is close to that of metal and a warp of the metallaminate is hard to occur, which is desirable.

The thermoplastic resin used in the insulating layer in the metallaminate of the present invention is not limited to a specificone.However, it is preferable that the thermoplastic resin is thermoplasticpolyimide obtained by polymerizing at least one diamine selected fromthe group consisting of 1,3-bis(3-aminophenoxy)benzene,1,3-bis(3-(3-aminophenoxy)phenoxy)benzene,4,4′-bis(3-aminophenoxy)biphenyl and 3,3′-diaminobenzophenon, and atleast one tetra-carboxylic dianhydride selected from the groupconsisting of pyromellitic dianhydride,3,3′,4,4′-biphenyl-tetra-carbocylic dianhydride, 3,3′,4,4′-benzophenontetra-carbocylic dianhydride, or3,3′,4,4′-diphenyl-ether-tetra-carbocylic dianhydride.

In case that the above-described thermoplastic polyimide is produced, itis preferable that are action mole ratio of diamine component andtetra-carbocylic dianhydride is in a rang of 0.75 to 1.25.

As specific examples of the constitution of the metal laminate of thepresent invention, there is a single-sided metal laminate where aninsulating layer has been laminated on a metal plate, or a double-sidedmetal laminate where an insulating layer and a metal plate areconstituted on another metal plate, and a preferable metal laminate is adouble-sided metal laminate comprising a metal layer/a polyimide layer/aSUS layer selected from the group consisting of copper, SUS and copperalloy.

When polyimide has been used as the insulating layer of the metallaminate, there is a wet etching process mainly using hydrazine or aplasma etching process as a polyimide etching process. Both theprocesses can be used, because there is not a significant differencebetween the both regarding a polyimide etching rate.

The present invention also provides a plasma etching process where themetal laminate is a material to be etched or a wet etching process of ametal laminate where the metal laminate is etched with alkaline aqueoussolution.

In order to remove the insulating layer of the metal laminate by theplasma etching process, it is preferable that a plasma machiningapparatus provided with a cathode electrode, an anode electrode and aplasma gas introducing pipe. As the plasma machining apparatus, forexample, a plasma machining apparatus disclosed in JP2000-293966Apublication can be used. As conditions of the plasma etching, thepressure of etching gas is preferably in a range of 3 to 50 Pa. Thecomponent of the etching gas comprises oxygen which is a main componentand SF₆ added thereto at a percentage of 10 to 20%. Further, the etchinggas may be added with Ar at a percentage of 5 to 15%. Furthermore,instead of SF₆, NF₃, CF₄, CHF₃ or the like may be used. The etching ispreferably conducted at a flow rate of the etching gas of about 30 to3000 sccm. The etching is preferably conducted with a power of 0.5 to 5W. In case that polyimide is used as the insulating layer of the metallaminate, the etching rate of polyimide is set to a value obtained bydividing a weight of the insulating layer by a time required forremoving the insulating layer completely when the etching has beenconducted under the above-described conditions.

In case that the insulating layer is removed by the wet etching process,strong alkaline aqueous solution can be used. As the strong alkalineaqueous solution, aqueous solution of potassium hydroxide with 2 to 50wt % can preferably be used. Specifically, alkali-amine type etchantdisclosed in JP10-97081A publication can be used. It is preferable thatetchant is heated to be used, and it is further preferable that etchantis heated to a temperature of about 60 to 90° C.

The etching rate in case that polyimide is used as the insulating layerof the metal laminate is set to a value obtained by dividing a weight ofthe insulating layer by a time required for performing etching withaqueous solution of potassium hydroxide with 30 wt % heated to 80° C. toremove the insulating layer completely.

In case that a plasma etching of the insulating layer is performed usinga metal laminate where the thickness of an oxide film of a metal is in arange of at least 0 Å and less than 50 Å, the etching rate is at least 5mg/min, which is desirable. When wet etching is conducted, the etchingrate becomes at least 2 mg/sec, which is desirable. When the etchingrate is smaller than the value, the so-called over-etching phenomenon isobserved, so that there will occur such a drawback that amicro-fabrication can not be substantially carried out.

For the method for manufacturing a metal laminate of the presentinvention, as one example of a case of using polyimide in an insulatinglayer and using SUS304 and copper alloy as metal, there are a methodwhich sequentially applying and curing thermoplasticpolyimide/non-thermoplastic polyimide/thermoplastic polyimide to acopper alloy foil and laminating SUS304 thereto by thermo-compressionbonding and a method which uses a double-sided adhesive sheet obtainedby applying thermoplastic polyimide to both surfaces of anon-thermoplastic polyimide film to laminate respective copper alloy andSUS304 thereto by thermo-compression bonding. Incidentally, as thethermo-compression bonding method, there are a thermal press, alaminating and the like.

In one of more specific manufacturing methods, there is the followingmethod. One portion of a thin strip of SUS304 which is metal is takenout from a roll thereof and its thickness is measured using AES. A thinstrip whose oxide film thickness is in a range of at least 0 Å and lessthan 50 Å is selected and used. Next, varnish including polyamic acidwhich is precursor of thermoplastic polyimide is applied on a copperalloy and drying/curing is conducted at a temperature of about 60 to400° C. to form a thermoplastic polyimide layer, varnish includingpolyamic acid which is precursor of non-thermoplastic polyimide isapplied on the thermoplastic polyimide layer and drying/curing isconducted at a temperature of 60 to 400° C. to form anotherthermoplastic polyimide layer, varnish including polyamic acid which isprecursor of thermoplastic polyimide is applied on the anotherthermoplastic polyimide and drying/curing is conducted at a temperatureof 60 to 400° C. to form still another thermoplastic polyimide layer,and a thermal compression bonding of SUS304 is then conducted on asurface of thermoplastic polyimide at a temperature of 150 to 600° C.;or varnish including polyamic acid which is precursor of thermoplasticpolyimide is applied on both surfaces of the non-thermoplastic polyimidefilm and drying/curing is conducted at a temperature of 60 to 400° C. toform a double-sided thermoplastic polyimide bonding sheet and thermalcompression bondings of copper alloy and SUS304 are conducted on theboth surfaces of the sheet at a temperature of 150 to 600° C.

A base film of a bonding sheet which can be used is not limited to aspecific one, but it is possible to use a non-thermoplastic polyimidefilm commercially available. As specific examples, there are UPILEX(trademark) Series of polyimide film manufactured by UBE INDUSTRIES,LTD, APICAL (trademark) Series of polyimide film manufactured by KANEKA,LTD, KAPTON (trademark) Series of polyimide film manufactured by DUPONT-TORAY CO., LTD, Aramica Series of polyimide film manufactured byTORAY INDUSTRIES, INC. and the like.

In the present invention, the thickness of the insulating layer ispreferably in a range of 5 to 250 μm, and more preferably in a range of8 to 50 μm. Preferable thicknesses of thermoplasticpolyimide/non-thermoplastic polyimide/thermoplastic polyimide which areused as the insulating layer are 0.5 μm to 10 μm/7.5 μm to 75 μm/0.5 μmto 10 μm, respectively.

In the metal laminate provided by the present invention, when SUS304 isused as metal, a polyimide etching rate after SUS304 has been etched canbe estimated based on the thickness of a surface oxide film of SUS304.Therefore, a polyimide etching time can be can be calculated in advanceso that the efficiency of a polyimide etching step can be improved.

According to the present invention, a metal laminate excellent inpolyimide etching property can be obtained. For this reason, thepolyimide laminate of the present invention is suitably used as asuspension particularly used in a hard disc.

A manufacturing method of a suspension for a hard disc can generally beconducted in the following manner.

First, a photosensitive resin is formed on a metal surface of the metallaminate plate of the present invention for forming a circuit byapplication or pasting. A mask on which a desired pattern image has beendrawn is brought in close contact with the photosensitive resin andmicrowaves with a wavelength where the photosensitive resin hassensitivity are irradiated on the photosensitive resin. A non-exposedportion of the photosensitive resin is eluted with predetermineddeveloper to from a desired circuit image on the metal. After exposedmetal has been solved by dipping the metal laminate in this state insolution which can solve metal such as ferric chloride or the like orspaying the solution on the substrate, the photosensitive resin isreleased by a predetermined releasing agent to form the circuit.

Next, similarly, a mask on which a desired pattern image has been drawnis brought in close contact with the circuit formed on the metal surfaceso that patterning is conducted by a wet etching process or a plasmaetching process.

After patterning has been completed, a suspension is fabricated byjoining the metal laminate to a stainless work product called “a loadbeam” by a laser welding or the like.

EXAMPLES

The present invention will be further explained below with reference toExamples.

A thickness of a surface oxide film of metal (SUS304), an insulatinglayer (polyimide) etching rate and an average thermal expansioncoefficient were measured by the following methods.

(1) Surface Oxide Film Measuring Method

Using an apparatus of MICROLAB310F manufactured by VG Inc. as AES (AugerElectron Spectroscopy), ion etching was conducted for a predeterminedtime under the conditions of an acceleration voltage of 5,00 KV, acurrent of 9.01×10⁻³⁰ A, a pressure of 2.1×10⁻⁸ Pa to analyze the kindsand the amounts of elements. A decrease of a film thickness due to theion etching was observed and length-measured by TEM. Thereby, thethickness of the surface oxide film could be obtained when atomicconcentrations of metal elements and oxygen element became equal to eachother.

(2) Polyimide Etching Rate (A Case of Plasma-Etching)

After SUS304 side of a double-sided metal laminate was removed usingferric chloride solution, a plasma etching processing was conducted. Thesingle-sided metal laminate obtained by removing SUS304 was thrown in achamber set to such conditions that O₂, SF₆ and Ar gas flow rates wererespectively 0.89 L/min, 0.19 L/min and 0.07 L/min, a pressure at thistime was 26.7 Pa, and a discharge output was 2.3 KW, and it was treatedfor 5 min. Weights of the single-sided metal laminate before and afterthe plasma etching were measured by an electronic force balance, and anetching rate was calculated.

(3) Polyimide Etching Rate (A Case of Wet-Etching)

After SUS304 side of a double-sided metal laminate was removed usingferric chloride solution, a wet etching was conducted. As etchant,TPE-3000 (trade name) manufactured by TORAY ENGINEERING CO., LTD. wasused. The etchant was heated to a temperature of 80° C. and stirred by amagnetic stirrer, and single-sided metal laminate obtained by removingSUS304 was thrown in the etchant and treated for one minute. Weights ofthe single-sided metal laminate before and after the plasma etching weremeasured by an electronic force balance, and an etching rate wascalculated.

(4) Thermal Expansion Coefficient

Measurement was conducted, using a thermo-mechanical analyzer TMA4000manufactured by MAC SCIENCE COMPANY, under the condition that a tensileload was 3 g, a temperature rising speed was 10° C./min, a temperaturerange was a range of 100° C. to 250° C., and thermal expansioncoefficients were calculated.

Further, abbreviations of solvent, acidic anhydride and diamine are asfollows:

-   DMAc: N,N′-dimethylacet-amide-   NMP: N-methyl-2-pyrrolidone-   PPD: p-phenylenediamine-   ODA: 4,4′-diamino diphenyl ether-   m-BP: 4,4′-bis(3-aminophenoxy)biphenyl-   APB: 1,3-bis(3-aminophenoxy)benzene-   APPB: 1,3-bis(3-(3-aminophenoxy)phenoxy)benzene-   DABP: 3,3′-diamino benzophenone-   BPDA: 3,3′,4,4′-biphenyl tetra-carboxylic dianhydride-   BTDA: 3,3′,4,4′-benzophenone tetra-carboxylic dianhydride-   PMDA: pyromellitic dianhydride

Synthetic Example 1

<Synthesis of Thermoplastic Polyimide Precursor>

20 moles of APB as a diamine component and 19.4 moles of BTDA astetra-carboxylic dianhydride component were weighed and they were mixedin solvent of N,N′-dimethylacet-amide. Mixing temperature and mixingtime were 23° C. and 8 hours. Further, the mixing was conducted in astate that a solid component concentration at a start time of the mixingwas 17 weight percent. The viscosity of polyamic acid varnish obtainedwas 400 cps at a temperature of 25° C. and was suitable for application.

Synthetic Example 2

<Synthesis of Thermoplastic Polyimide Precursor>

20 moles of DABP as a diamine component and 19.4 moles of BTDA astetra-carboxylic dianhydride component were weighed and they were mixedin solvent of N,N′-dimethylacet-amide. Mixing temperature and mixingtime were 23° C. and 8 hours. Further, the mixing was conducted in astate that a solid component concentration at a start time of the mixingwas 17 weight percent. The viscosity of polyamic acid varnish obtainedwas 300 cps at a temperature of 25° C. and was suitable for application.

Synthetic Example 3

<Synthesis of Thermoplastic Polyimide Precursor>

20 moles of APB as a diamine component and 19.4 moles of BPDA astetra-carboxylic dianhydride component were weighed and they were mixedin solvent of N,N′-dimethylacet-amide. Mixing temperature and mixingtime were 23° C. and 8 hours. Further, the mixing was conducted in astate that a solid component concentration at a start time of the mixingwas 17 weight percent. The viscosity of polyamic acid varnish obtainedwas 400 cps at a temperature of 25° C. and was suitable for application.

Synthetic Example 4

<Synthesis of Thermoplastic Polyimide Precursor>

20 moles of m-BP as a diamine component and 9.8 moles of each of BPDAand PMDA as tetra-carboxylic dianhydride component were weighed and theywere mixed in solvent of N-methyl-2-pyrrolidone. Mixing temperature andmixing time were 23° C. and 8 hours. Further, the mixing was conductedin a state that a solid component concentration at a start time of themixing was 15 weight percent. The viscosity of polyamic acid varnishobtained was 500 cps at a temperature of 25° C. and was suitable forapplication.

Synthetic Example 5

<Synthesis of Thermoplastic Polyimide Precursor>

20 moles of APPB as a diamine component and 19.4 moles of BTDA as atetra-carboxylic dianhydride component were weighed and they were mixedin solvent of N,N′-dimethylacet-amide. Mixing temperature and mixingtime were 23° C. and 8 hours. Further, the mixing was conducted in astate that a solid component concentration at a start time of the mixingwas 17 weight percent. The viscosity of polyamic acid varnish obtainedwas 400 cps at a temperature of 25° C. and was suitable for application.

Synthetic Example 6

<Synthesis of Non-Thermoplastic Polyimide Precursor>

7.7 moles of PPD, 1.15 moles of ODA and 1.15 moles of m-BP as a diaminecomponent were weighed. 5.4 moles of BPDA and 4.45 moles of PMDA astetra-carboxylic dianhydride component were weighed. These componentswere dissolved and mixed in mixed solvent of N,N′-dimethylacet-amide andN-methyl-2-pyrrolidone. The solvent ratio of the former to the latterwas 23 weight percent: 77 weight percent. As a result of measurementconducted by an E type viscometer, the viscosity of polyamic acidvarnish obtained was 30000 cps at a temperature of 25° C. and wassuitable for application.

Example 1

<Measurement of Thickness of Metal Oxide Film>

An oxide film thickness of a stainless steel foil (Trade Name:SUS304H-TA with thickness of 20 μm, manufactured by NIPPON STEELCORPORATION) which was metal used for metal laminate was measured. Thethickness was 30 Å and it was suitable for etching an insulating layer.

<Manufacture of Single-Sided Metal Laminate>

After a polyamic acid varnish of the synthetic example 2 as athermoplastic polyimide layer was applied to a commercially availablecopper alloy foil (TradeName: C7025 (specially ordered brand) withthickness of 18 μm, manufactured by OLIN CORPORATION) and dried, andthen, after a polyamic acid varnish of the synthetic example 6 as anon-thermoplastic polyimide layer was applied to the dried varnish anddried, a polyamic acid varnish of the synthetic example 1 was appliedand dried to produce a single-sided metal laminate. A reverse rollcoater was used for the application of the thermoplastic polyamic acidvarnish and a die coater was used for the application of thenon-thermoplastic polyamic acid varnish. The thickness of the polyimidelayer after applied and dried was 13 μm. Incidentally, the maximumtemperature during drying was 350° C.

<Implementation of Heat Press>

A stainless steel foil (Trade Name: SUS304H-TA with thickness of 20 μm,manufactured by NIPPON STEEL CORPORATION) was used as metal. Asingle-sided metal laminate whose polyimide face was superimposed withthe SUS304H-TA foil was sandwiched between cushion materials (TradeName: KINYO BOARD F200, manufactured by KINYOSHA CO., LTD), and aheating and compressing adhering operation was conducted for 30 minutesunder the condition of 230° C. and 60 kg/cm² by a heating press machineto fabricate a polyimide metal laminate comprising five layers ofSUS304H-TA/themoplastic polyimide/non-thermoplasticpolyimide/thermoplastic polyimide/C7025.

<Evaluation of Polyimide Metal Laminate>

Using the polyimide metal laminate obtained, the surface oxide filmthickness and the polyimide etching rate according to the plasma etchingprocess were measured, as described above. As a result, the polyimideetching rate was 25 mg/min. A sectional configuration which did notinclude over-etching was obtained.

Example 2

<Manufacture of Double-Sided Adhesive Sheet>

Polyamic acid varnish of the synthetic example 1 as a non-thermoplasticpolyimide layer was applied to both surfaces of a commercially availablepolyimide film (Trade Name: APICAL® 12.5NPI with thickness of 12.5 μm,manufactured by KANEKA, LTD) and dried to produce a double-sidedadhesive sheet. A reverse roll coater was used for the application ofthe thermoplastic polyamic acid varnish, and the thickness of thevarnish after applied and dried was 18 μm. Incidentally, the maximumtemperature during drying was 280° C.

<Measurement of Oxide Film Thickness>

An oxide film thickness of a stainless steel foil (Trade Name:SUS304H-TA with thickness of 20 μm, manufactured by NIPPON STEELCORPORATION) which was used for a metal laminate was measured. Thethickness was 40 Å and it was suitable for etching an insulating layer.

<Implementation of Heat Press>

A copper alloy foil (Trade Name: C7025 (specially ordered brand) withthickness of 18 μm, manufactured by OLIN CORPORATION) and a stainlesssteel foil (Trade Name: SUS304H-TA with thickness of 20 μm, manufacturedby NIPPON STEEL CORPORATION) were used as metal. A double-sided adhesivesheet whose both sides were respectively superimposed with C7025 andSUS304H-TA foils was sandwiched between cushion materials (Trade Name:KINYO BOARD F200 manufactured by KINYOSHA CO., LTD), and a heating andcompressing adhering operation was conducted for 60 minutes under thecondition of 250° C. and 70 kg/cm² by a heating press machine tofabricate a polyimide metal laminate comprising five layers ofSUS304H-TA/themoplastic polyimide/non-thermoplasticpolyimide/thermoplastic polyimide/C7025.

<Evaluation of Polyimide Metal Laminate>

Using the polyimide metal laminate obtained, the surface oxide filmthickness and the polyimide etching rate according to the plasma etchingprocess were measured, as described above. As a result, the surfaceoxide film thickness of SUS304H-TA coming in contact with polyimide was40 Å. As a result of plasma etching conducted from the SUS304 side, thepolyimide etching rate was 15 mg/min. A configuration which did not haveany over-etching was obtained.

Example 3

<Manufacture of Double-Sided Adhesive Sheet>

A double-side adhesive sheet was manufactured in the same manner as thatin Example 2 except that a thermoplastic polyimide precursor of thesynthetic example 3 was used instead of the thermoplastic polyimideprecursor of the synthetic example 1.

<Measurement of Oxide Film Thickness>

An oxide film thickness of a stainless steel foil (Trade Name:SUS304H-TA with thickness of 20 μm, manufactured by NIPPON STEELCORPORATION) which was used for a metal laminate was measured. Thethickness was 35 Å and it was suitable for etching an insulating layer.

<Implementation of Heat Press>

A polyimide metal laminate comprising five layers ofSUS304H-TA/themoplastic polyimide/non-thermoplasticpolyimide/thermoplastic polyimide/C7025 was produced in the same manneras that in Example 2 except that a heating and compressing adheringoperation was conducted for 30 minutes under the conditions of 270° C.and 50 kg/cm² by a heating press machine.

<Evaluation of Polyimide Metal Laminate>

Using the polyimide metal laminate obtained, plasma etching wasconducted from the SUS304 side and measurement was carried out, asdescribed above. As a result, the polyimide etching rate was 18 mg/min.A configuration which did not have any over-etching was obtained.

Example 4

<Manufacture of Double-Sided Adhesive Sheet>

A double-side adhesive sheet was manufactured in the same manner as thatin Example 2 except that a thermoplastic polyimide precursor of thesynthetic example 4 was used instead of the thermoplastic polyimideprecursor of the synthetic example 1.

<Measurement of Oxide Film Thickness>

An oxide film thickness of a stainless steel foil (Trade Name:SUS304H-TA with thickness of 20 μm, manufactured by NIPPON STEELCORPORATION) which was used for a metal laminate was measured. Thethickness was 47 Å and it was suitable for etching an insulating layer.

<Implementation of Heat Press>

A polyimide metal laminate comprising five layers ofSUS304H-TA/themoplastic polyimide/non-thermoplasticpolyimide/thermoplastic polyimide/C7025 was produced in the same manneras that in Example 2 except that a heating and compressing adheringoperation was conducted for 60 minutes under the conditions of 290° C.and 50 kg/cm² by a heating press machine.

<Evaluation of Polyimide Metal Laminate>

Using the polyimide metal laminate obtained, plasma etching wasconducted from the SUS304 side and measurement of the polyimide etchingrate was carried out, as described above. As a result, the polyimideetching rate was 7 mg/min. A sectional configuration which over-etchingwas reduced was obtained.

Example 5

<Manufacture of Double-Sided Adhesive Sheet>

A double-sided adhesive sheet was manufactured in the same manner asthat in Example 2 except that a thermoplastic polyimide precursor of thesynthetic example 5 was used instead of the thermoplastic polyimideprecursor of the synthetic example 1.

<Measurement of Oxide Film Thickness>

An oxide film thickness of a stainless steel foil (Trade Name:SUS304H-TA with thickness of 20 μm, manufactured by NIPPON STEELCORPORATION) which was used for a metal laminate was measured. Thethickness was 450 Å and it was suitable for etching an insulating layer.

<Implementation of Heat Press>

A polyimide metal laminate comprising five layers ofSUS304H-TA/themoplastic polyimide/non-thermoplasticpolyimide/thermoplastic polyimide/C7025 was produced in the same manneras that in Example 2 except that a heating and compressing adheringoperation was conducted for 30 minutes under the conditions of 230° C.and 50 kg/cm²by a heating press machine.

<Evaluation of Polyimide Metal Laminate>

Using the polyimide metal laminate obtained, plasma etching wasconducted from the SUS304 side and the polyimide etching rate wasmeasured, as described above. As a result, the polyimide etching ratewas 10 mg/min.

Example 6

<Manufacture of Single-Sided Metal Laminate>

After a polyamic acid varnish of the synthetic example 3 as athermoplastic polyimide layer was applied to a commercially availablecopper alloy foil (Trade Name: C7025 with thickness of 18 μm,manufactured by OLIN CORPORATION) and dried, and then, after a polyamicacid varnish of the synthetic example 4 as a non-thermoplastic polyimidelayer was applied to the dried varnish and dried, a polyamic acidvarnish of the synthetic example 1 was applied and dried to produce asingle-sided metal laminate. A reverse roll coater was used for theapplication of the thermoplastic polyamic acid varnish and a die coaterwas used for the application of the non-thermoplastic polyamic acidvarnish. The thickness of the polyimide layer after applied and driedwas 13 μm. Incidentally, the maximum temperature during drying was 350°C.

<Measurement of Oxide Film Thickness>

An oxide film thickness of a stainless steel foil (Trade Name:SUS304H-TA with thickness of 20 μm, manufactured by NIPPON STEELCORPORATION) which was used for a metal laminate was measured. Thethickness was 32 Å and it was suitable for etching an insulating layer.

<Implementation of Heat Press>

As a stainless steel foil, Trade Name: SUS304H-TA with thickness of 20μm, manufactured by NIPPON STEEL CORPORATION was used. A single-sidedmetal laminate whose polyimide face was superimposed with the SUS304H-TAfoil was sandwiched between cushion materials (Trade Name: KINYO BOARDF200, manufactured by KINYOSHA CO., LTD), and a heating and compressingadhering operation was conducted for 30 minutes under the conditions of230° C. and 60 kg/cm² by a heating press machine to fabricate apolyimide metal laminate comprising five layers ofSUS304H-TA/themoplastic polyimide/non-thermoplasticpolyimide/thermoplastic polyimide/C7025.

<Evaluation of Polyimide Metal Laminate>

Using the polyimide metal laminate obtained, wet etching was conductedfrom the SUS304 side and the polyimide etching rate and the thermalexpansion coefficient were measured, as described above. As a result,the polyimide etching rate was 3.4 mg/min and the thermal expansioncoefficient was 20 ppm/° C. A sectional configuration which had reducedover-etching was obtained.

Example 7

<Manufacture of Double-Sided Adhesive Sheet>

Polyamic acid varnish of the synthetic example 2 as a non-thermoplasticpolyimide layer was applied to both surfaces of a commercially availablepolyimide film (Trade Name: APICAL 12.5NPI with thickness of 12.5 μm,manufactured by KANEKA, LTD) and dried to produce a double-sidedadhesive sheet. A reverse roll coater was used for the application ofthe thermoplastic polyamic acid varnish, and the thickness of thevarnish after applied and dried was 18 μm. Incidentally, the maximumtemperature during the drying was 260° C.

<Measurement of Oxide Film Thickness>

An oxide film thickness of a stainless steel foil (Trade Name:SUS304H-TA with thickness of 20 μm, manufactured by NIPPON STEELCORPORATION) which was used for a metal laminate was measured. Thethickness was 45 Å and it was suitable for etching an insulating layer.

<Implementation of Heat Press>

A copper alloy foil (Trade Name: C7025 (specially ordered brand) withthickness of 18 μm, manufactured by OLIN CORPORATION) and a stainlesssteel foil (Trade Name: SUS304H-TA with thickness of 20 μm, manufacturedby NIPPON STEEL CORPORATION) were used as metal. A double-sided adhesivesheet whose both sides were respectively superimposed with C7025 andSUS304H-TA foils was sandwiched between cushion materials (Trade Name:KINYO BOARD F200 manufactured by KINYOSHA CO., LTD), and a heating andcompressing adhering operation was conducted for 60 minutes under thecondition of 250° C. and 70 kg/cm² by a heating press machine tofabricate a polyimide metal laminate comprising five layers ofSUS304H-TA/themoplastic polyimide/non-thermoplasticpolyimide/thermoplastic polyimide/C7025.

<Evaluation of Polyimide Metal Laminate>

Using the polyimide metal laminate obtained, wet etching was conductedfrom the SUS304 side and the polyimide etching rate and the thermalexpansion coefficient were measured, as described above. As a result,the polyimide etching rate was 5.7 mg/min and the thermal expansioncoefficient was 22 ppm/° C.

Comparative Example 1

<Manufacture of Double-Sided Adhesive Sheet>

Polyamic acid varnish of the synthetic example 2 as a non-thermoplasticpolyimide layer was applied to both surfaces of a commercially availablepolyimide film (Trade Name: APICAL 12.5NPI with thickness of 12.5 μm,manufactured by KANEGAFUCHI KAGAKU, LTD) and dried to produce adouble-sided adhesive sheet. A reverse roll coater was used for theapplication of the thermoplastic polyamic acid varnish, and thethickness of the varnish after applied and dried was 18 μm.Incidentally, the maximum temperature during drying was 260° C.

<Measurement of Oxide Film Thickness>

An oxide film thickness of a stainless steel foil (Trade Name: SUS

304H-TA with thickness of 20 μm, manufactured by NIPPON STEELCORPORATION) which was used for a metal laminate was measured. Thethickness was 82 Å and the surface oxide film was thick.

<Implementation of Heat Press>

A copper alloy foil (Trade Name: C7025 (specially ordered brand) withthickness of 18 μm, manufactured by OLIN CORPORATION) and a stainlesssteel foil (Trade Name: SUS304H-TA with thickness of 20 μm, manufacturedby NIPPON STEEL CORPORATION) were used as metal. A double-sided adhesivesheet whose both sides were respectively superimposed with C7025 andSUS304H-TA foils was sandwiched between cushion materials (Trade Name:KINYO BOARD F200 manufactured by KINYOSHA CO., LTD), and a heating andcompressing adhering operation was conducted for 60 minutes under thecondition of 250° C. and 70 kg/cm² by a heating press machine tofabricate a polyimide metal laminate comprising five layers ofSUS304H-TA/themoplastic polyimide/non-thermoplasticpolyimide/thermoplastic polyimide/C7025.

<Evaluation of Polyimide Metal Laminate>

Using the polyimide metal laminate obtained, wet etching was conductedfrom the SUS304 side and the polyimide etching rate and the thermalexpansion coefficient were measured, as described above. As a result,the polyimide etching rate was 1.2 mg/min and the thermal expansioncoefficient was 22 ppm/° C.

There occurred no warp in the base plate and a drawback about appearancewas not found. However, since the etching rate was slow, a sectionalconfiguration after etching became trapezoidal and over-etching occurredso that a desired shape can not be obtained.

Industrial Applicability

As a metal laminate of the present invention, a polyimide metal laminatehaving a constitution of copper alloy/polyimide/SUS304 is provided asone example. In the case, the metal laminate is a polyimide metallaminate where a polyimide etching rate after SUS304 has been etched canbe estimated by measuring a surface oxide film of SUS304 existing in alamination interface between polyimide and SUS304. For this reason, anetching time of polyimide in the polyimide metal laminate can becalculated and a flexure used in a suspension of a hard disc drivehaving a high productivity can be provided.

1. A metal laminate comprising a metal layer laminated to an insulatinglayer, where the insulating layer is subjected to an etching processing,wherein, in a surface of the metal layer which is in contact with theinsulating layer, respective concentrations of main metal element andoxygen element constituting the metal layer are measured from thesurface of the metal layer towards the inside of the metal layer in atime-elapsing manner according to AES (Auger electron spectroscopy) andof the thickness of a metal oxide film of the surface of the metal layermeasured at a time when atomic concentrations of the main metal elementand the oxygen element constituting the metal layer equal to each otheris in a range of at least 0 Å to less than 50 Å.
 2. The metal laminateaccording to claim 1, wherein the metal layer includes at least oneelement selected from the group consisting of iron element, copperelement, aluminum element, nickel element and molybdenum element.
 3. Themetal laminate according to claim 1, wherein the insulating layer is aresin selected from the group consisting of polyimide, polyamide,polyamideimide.
 4. The metal laminate according to claim 1, wherein themetal laminate is a double-sided metal laminate comprising a SUS layer/apolyimide layer/a metal layer selected from the group consisting ofcopper, SUS and copper alloy.
 5. The metal laminate according to claim4, wherein the polyimide layer comprises thermoplastic polyimidelayer/non-thermoplastic polyimide layer/thermoplastic polyimide layer.6. A flexure for a suspension for a hard disc, manufactured from a metallaminate according to claim
 5. 7. (canceled)
 8. A plasma etching methodcomprising etching a metal laminate according to claim
 5. 9. A wetetching method comprising etching a metal laminate according to claim 5with alkaline aqueous solution.
 10. A flexure for a suspension for ahard disc, manufactured from a metal laminate according to claim
 4. 11.A flexure for a suspension for a hard disc, manufactured from a metallaminate according to claim
 3. 12. A flexure for a suspension for a harddisc, manufactured from a metal laminate according to claim
 2. 13. Aflexure for a suspension for a hard disc, manufactured from a metallaminate according to claim
 1. 14. A plasma etching method comprisingetching a metal laminate according to claim
 4. 15. A plasma etchingmethod comprising etching a metal laminate according to claim
 3. 16. Aplasma etching method comprising etching a metal laminate according toclaim
 2. 17. A plasma etching method comprising etching a metal laminateaccording to claim
 1. 18. A wet etching method comprising etching ametal laminate according to claim 4 with alkaline aqueous solution. 19.A wet etching method comprising etching a metal laminate according toclaim 3 with alkaline aqueous solution.
 20. A wet etching methodcomprising etching a metal laminate according to claim 2 with alkalineaqueous solution.
 21. A wet etching method comprising etching a metallaminate according to claim 1 with alkaline aqueous solution.
 22. Amethod for manufacturing a metal laminate comprising laminating a metallayer to an insulating layer where the insulating layer is to besubjected to an etching processing, wherein the metal layer is selectedso that the surface of the metal layer which is in contact with theinsulating layer, has a thickness of a metal oxide film of the surfaceof the metal layer measured at a time when atomic concentrations of themain metal element and the oxygen element constituting the metal layerare equal to each other in a range of at least 0 Å to less than 50 Å,the respective concentrations of main metal element and oxygen elementconstituting the metal layer being measured from the surface of themetal layer towards the inside of the metal layer in a time-elapsingmanner according to AES (Auger electron spectroscopy).